Suddenly think [name_f]Callia[/name_f], nickname [name_u]Cali[/name_u] is gorgeous! [name_u]Seren[/name_u] is my other current favourite. Tbh I have to have middle name [name_f]Cecilia[/name_f] for my late Mum, so I think that rules out [name_f]Callia[/name_f] anyway ”. But still nice to think of.
I think the name [name_f]Callia[/name_f] is so close to your mom’s name that it honours her memory without using her name. Or use [name_f]Callia[/name_f] along with a middle that is your mom’s middle name, favourite flower or something else significant to honour her.
[name_f]Callia[/name_f] could be an honour for you mum and you, if you were up for that. It’s nice though i do prefer the soft, starry feel that [name_u]Seren[/name_u] has
[name_m]Hi[/name_m] there.
[name_f]Callia[/name_f] is very pretty. I’d personally spell the nn [name_f]Callie[/name_f], since the two 'l’s makes more sense to me. [name_u]Seren[/name_u] is not my style, but it’s interesting & kind of cool. Certainly not awful, & [name_u]Seren[/name_u] [name_f]Cecilia[/name_f] has a nice flow. If you still wanted to try to get [name_u]Cali[/name_u]/[name_f]Callie[/name_f], how about [name_f]Calliope[/name_f] [name_f]Cecilia[/name_f]? That sounds lovely!
[name_f]Hope[/name_f] this helps. 
I do prefer [name_u]Seren[/name_u], it just has a very lovely and unique sound.
But [name_f]Callia[/name_f] is fun and spunky too! And nickname [name_f]Callie[/name_f] is sweet. I also agree that it could honor your mom.
[name_u]Seren[/name_u] is my favourite and I love [name_u]Seren[/name_u] [name_f]Cecilia[/name_f]
Using [name_f]Cecilia[/name_f] I think does sound too similar to [name_f]Callia[/name_f] to be used together. Perhaps if you have a second girl. I think [name_u]Seren[/name_u] [name_f]Cecilia[/name_f] does work together. She could go by [name_f]Sera[/name_f] or [name_u]Ren[/name_u].
[name_f]Calla[/name_f] [name_f]Cecilia[/name_f] might work a little better? Or you could use [name_f]Cecilia[/name_f] nn [name_u]Cali[/name_u]?
Having said all of that, I really adore [name_u]Seren[/name_u] and it’s just beautiful with [name_f]Cecilia[/name_f]. That’s what I’d go for probably.